1. Field of the Invention
The present invention relates to a magnetic balance type current sensor utilizing a magnetoresistance effect element.
2. Description of the Related Art
The intensity of a current used for driving a motor in an electric automobile is detected by, for example, a current sensor. As such a current sensor, there is a magnetic balance type current sensor. In the magnetic balance type current sensor, if a current to be measured flows, an output voltage occurs in a magnetic detecting element owing to an induction magnetic field according to the current, and a voltage signal output from the magnetic detecting element is converted into a current and fed back to a feedback coil. In addition to this, an operation is performed so that a magnetic field (cancelling magnetic field) occurring owing to the feedback coil and the induction magnetic field occurring owing to the current to be measured cancel out each other and hence a magnetic field constantly becomes zero. At this time, a feedback current flowing through the feedback coil is subjected to voltage conversion and extracted as an output.
As a magnetic detecting element in the above-mentioned magnetic balance type current sensor, for example, a magnetoresistance effect element such as a Giant Magneto Resistance (GMR) element is used. An example of such a magnetic detecting element is described in Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2000-516714. In such a magnetic balance type current sensor, a magnetic shield is provided that is used for attenuating the induction magnetic field due to the current to be measured and enhancing the cancelling magnetic field.